This invention relates to the fabrication of improved semiconductor devices and especially to improved FET devices.
It has been found that a retrograde or gradient channel carrier concentration (with respect to depth of the concentration) improves the linearity and noise figures of GaAs transistors. Furthermore, the gain of such transistors is greatly improved by the existence of a hyperabrupt interface between the active and the underlying layers. However, the achievement of these conditions requires expensive fabrication techniques such as molecular beam epitaxy. This invention provides for achievement of these conditions by easy, inexpensive ion-implantation techniques.